Fast degradable polyester polymer and preparation method and use thereof

ABSTRACT

A rapidly degradable polyester polymer and its preparation methods and applications are disclosed. The polyester polymer of the present invention is made by poly-condensation of repeat structure units, each of which consists of a non-degradable block A and degradable block B. The polyester polymer not only has good machinery processing performance, but also can be quickly degraded in appropriate of environment, thereby effectively resolve the environment pollution problems resulted in the used of polyester polymers. It satisfies the wide application demands and especially ensures such polymer can be used for beverage bottle, food package films, shopping bags and other food package containers. In addition, the method of preparation in present invention is simple, low-cost, and the raw materials are easily obtainable at low price. It is suitable for volume production and has practical value and application potentials.

FIELD OF THE INVENTION

The present invention relates to the preparation methods andapplications of a rapid degradable polyester polymer. More particularly,the invention relates to the preparation and applications ofcondensation-type copolyesters by embedding with small biodegradablesegments in the polymer main chains. It is belong to the field offunctional polymer materials.

BACKGROUND OF THE INVENTION

Polyesters are the general name of the polymers prepared by condensationpolymerization of polyol (poly alcohol) with poly acids. The typicalpolyester is aromatic polyester that is represented by polyethyleneterephthalate (PET), which is widely used in various industries offibers, packaging and others for its excellent chemical stability,proper mechanical properties and transparency and health performance. Atpresent time, polyester production and sales growth momentum remainsstrong, especially in the field of packaging of carbonate drinks. Withthe breakthrough of research on polyester's resistance properties, theapplications in the field of beer, food and cosmetic packaging willenlarge the market of polyesters. However, the polyester (PET) waste isdifficult to degrade naturally in nature. In the environment of humidityof 45% -100% , and temperature of 20° C. the PET bottles can exists for30-40 years, and its mechanical properties loss only 50%; at the sameconditions, the polyester film can exists as long as 90-100 years.Therefore, the huge amount of polyester waste will bring us tremendouspressure to the environment.

Recycling polyester waste is a prioritized method used in the worldbecause it can solve environmental problems and meanwhile fully utilizeresources. Various recycling technologies have been developed for PETfamily recycling. The simple way to recycle polyester waste can bepurified after the cleaning treatment, re-melting it and re-processingit into a relatively low-grade product, such as toys, detergent bottles:to re-produce high-grade polyester, the polyester need to be degraded,re-polymerized or used as chemical raw materials because the polyesteris a poly-condensed macromolecular material. In addition, there arepetroleumization technology, fuel recycling technology, incinerationtogether with other waste, and other energy recycling technologies.

But recycling and re-utilization of polyester waste cannot become thefinal solution for environment pollutions. The first reason is thelimitation of re-utilizing polyester waste, because it contains a lot ofadditives or other impurities that cannot be removed or it isregenerated polyesters already, thus it is very difficult to reutilizeit. Secondly, many polyester products are not suitable to be collectedand recycled, such as agriculture film, garbage bags, etc. Finally, itmay not worth to recycle those products if they cost too much or are notvaluable. Therefore, it is necessary to modify the degradability of suchpolyesters, make them degradable into small molecules in certain time atnatural conditions and finally return back to the recirculation ofnature.

It will be very beneficial for promoting polyesters long-termdevelopment if the lifetime of polyester in presence of nature can beeffectively controlled and therefore avoid contamination of itsenvironment, which makes PET-based polyester materials environmentfriendly.

The chemical factors may affect the degradability of materials includehydrophilicity, morphology, molecular mass, polymer composition, andetc. The stronger hydrophilicity of polymer is, the easier hydrolysiswill be, and it also will favor to be biodegraded by micro-organism.Hydrolysis enzyme likes to attack ester bond, amide bond and aminocarboxylic acid bond; the amorphous domains of polymer are easily to bedamaged by water and micro-organism than the crystal domains of polymerto be. Polymers with soft chains and low glass-transition temperatureare more easily to be degraded and the degradability of polymersincreases with the decreasing of molecular weight of polymers. Thecomposition of polymers, such as blend polymers and copolymer, also canaffect its degradation performance.

PET polyester contains ester bonds which are easily to be damaged bymicro-organism enzyme and water. At molten state, trace amount ofmoisture can cause rapid breaking of polyester bonds. In the processingand production of polyester, the moisture content of the resin must bestrictly controlled. However, under normal conditions, PET polyester hasgood chemical stability; it is difficult to be degraded under naturalconditions. This could be attributed to the regularity of structure ofPET polymer main chain, and the aromatic rings contained in the mainchain of PET. Existing of aromatic rings increased the polarity thepolymer chains with regularity, which lower its flexibility and improveits crystallization performance. High crystallinity of polymer can playa role of resisting hydrolysis because the water molecules are blockedto enter crystallization phase. PET is half crystallized polymer, itsinitial stage of degradation occurs in those domains of amorphous withrelative loose structure and the edges of half crystallized domains. Thehydrolysis and breaking of molecular chain segments betweenmicro-particles of crystal will result in molecular chains in amorphousfurther crystalline, making crystallinity obviously to increase, therebyhindering the occurring of further hydrolysis. On the other hand,increasing of rigidity of molecular chain will lower the movingactivities of macromolecules. It could be characterized by a higherglass-transition temperature, and therefore reduces the sensitivity ofpolymers to hydrolysis. Therefore, unlike the molten status, solid-statedegradation is a complex process which depends on activities of polymerchain and its penetrating capability.

Based on the above analysis for control factors of degradability of PETpolyester, it is necessary to lower the crystallization capability andglass-transition temperature for improving degradability of PETpolyester. The decrease of glass-transition temperature of polyester canalso increase the mobility of polymer chain segments and reduce theenergy needed for changing states, thereby increasing susceptibility tohydrolysis of polyester. Lower crystallinity can make water molecules ormicrobes effectively penetrate into material inner and attack its weakester bond.

Ways to reduce PET crystallinity can be either through controlling thelate stage of polymer materials processing, or through molecular designconcept, in some extent to reverse the polarity of PET polymer to morerigid structured architecture. By introducing third structure unit thatis flexible or contains specific functional group, the crystallizationproperties of PET can be changed radically. The methods to introducethird structure unit mainly are co-polymerization with addition ofmodifier and reactive blend with aliphatic polyesters.

Although it is clear theoretically the approaches for PET categoryaromatic polyesters, the applications are still very limited inpractical production. As PET category polyesters are widely appliedmaterials in the synthetic resin, studying its degradability mayeliminate the impact of their waste on the environment, and it will bevery meaningful for its long term development.

DETAILED DESCRIPTION OF THE INVENTION

In order to resolve above problems for existing technologies, theobjective of the present invention is to provide one kind of rapiddegradable polyester polymers and the preparation methods andapplications thereof, in order to reach the goal of rapid degradation atspecial conditions for polyester polymers such as PET and resolve theenvironment pollution problems resulted from the application of suchtype of polymers.

For the purpose of above objectives of invention, the technicalapproaches used in the present invention are as following: In oneaspect, the present invention provide a kid of rapid degradablepolyester polymers, with the repeat units consisting of non-degradablechain blocks A and degradable blocks B, obtained by condensationpolymerization and these polyester polymers have formula of (-AB—)_(n);with characters as:

In some embodiments, the non-degradable blocks have a structureaccording to Formula (I):

In some embodiments, the degradable blocks have a structure according toFormula (II):

In some embodiments, the polyester polymers (-AB—)_(n) have a structureaccording to Formula (III):

wherein

p, m, s, r and u are integers greater than 0 but smaller than 11;

t is an integer greater than 1 but smaller than 31;

n is an integer greater than 1;

R, R₁, R₂, R₃, R₄, R₅, R₆, R₇ are members independently selected in eachof the structural units from H, substituted or un-substituted alkyl,substituted or un-substituted heteroalkyl, substituted or un-substitutedcycloalkyl, substituted or un-substituted heterocycloalkyl, substitutedor un-substituted aryl and substituted or un-substituted heteroaryl,substituted or un-substituted alkoxy, ester, nitro, amine, amide, orthiol.

In some embodiments, R, R₁, R₂, R₃, R₄, R₅, R₆, are independentlyselected in each of the structural units from H or C₁-C₁₀ alkyls; R₇ isselected from H, substituted or un-substituted alkyl, substituted orun-substituted heteroalkyl, substituted or un-substituted cycloalkyl,substituted or un-substituted heterocycloalkyl, substituted orun-substituted aryl.

In some embodiments, R, R₁, R₂, R₃, R₄, R₅, R₆, are independentlyselected in each of the structural units from H or methyl, ethyl,propyl, isopropyl, butyl, isobutyl, tert-butyl; R₇ is selected from H,substituted or un-substituted alkyl, substituted or un-substitutedheteroalkyl, substituted or un-substituted cycloalkyl, substituted orun-substituted heterocycloalkyl.

In some embodiments, the R is methyl; R₁, R₂, R₃, R₄, R₅, R₆, R₇ are H;p=2; m and s are any integer independently selected from 1, 2, 3, 4, 5;t is an integer greater than 1 but smaller than 31; r=1 or 2; u=1 or 2;and n is an integer greaer than 2.

In another aspect, the present invention provides a preparation methodfor manufacturing rapid degradable polyester polymers as following:

a) Organic Synthesis of degradable blocks B:

b) Condensation polymerizing non-degradable blocks A and degradableblocks B through solution polymerization or bulk polymerization:

where the definition of R, R₁, R₂, R₃, R₄, R₅, R₆, R₇ and p, m, s, r, u,t, n are the same as above; X is selected from Cl, Br, I, NH₂ or OH.

In some embodiments, the synthesis of non-degradable blocks A consistsof following steps:

In some embodiments, another preparation method of making rapiddegradable polyester polymers is as follows:

where the definition of R, R₁, R₂, R₃, R₄, R₅, R₆, R₇ and p, m, s, r, u,t, n are the same as above.

In further embodiments, synthesis of

includes the following steps:

In order to ensure the degradable blocks to be distributed evenly alongthe polymer main chains, the non-degradable blocks or oligmers will besynthesized first through melting condensation polymerization (e.g.react under vacuum at 240-290° C. for 2-7 hours), then the degradableblocks are added to continue the melting condensation polymerization(e.g. continue the reaction under vacuum at 240-290° C. for 2-7 hours).

To obtain higher molecular weight polymers, it is achievable as long asthe moles of non-degradable blocks are larger than the moles ofdegradable blocks. Because the ethylene glycol in the excessive amountof non-degradable blocks can be removed under vacuum at hightemperature, a self-condensation polymerization to form high molecularpolymers is possible.

Compare to the existing technologies, the polyester polymers disclosedin present invention embraced different structured degradable blocksalong the polymer main chains and therefore reduced its crystallinity,make its melting temperature much lower than that of regular polyesterpolymers. In addition, due to embraced degradable blocks, soft segmentsof polymer become longer, and the glass-transition temperature of thepolymer is lower than that of regular polyester polymers also. Thus, thepolyester polymers of the present invention not only have excellentprocessing properties, but also can be degraded quickly into many shortnon-degradable chains in proper environment (such as alkalinesolutions), followed by further complete degradation of non-degradableshort segments. It effectively resolved the problems of environmentpollution resulted from applications of such kind of polymers andsatisfied the need of wide applications of such kind of polymers.Especially, it can ensure such kind of polymers be used for beveragebottle, food package film, shopping bags and other food packagecontainers. In addition, the method of preparation in present inventionis simple, low-cost, and the raw materials are easy to be obtained atlow price. It is suitable to volume production and has practical valueand application potentials.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is the DSC curve for polyester mPET(MeGSGMe) prepared in example1.

FIG. 2 is the degradation curve for polyester mPET(MeGSGMe) prepared inexample 1.

FIG. 3 is the relationship of intrinsic viscosity vs polymerization timefor PET oligmers prepared in example 2.

EMBODIMENTS

The following examples are detailed demonstrations of present invention.All of the following experiment methods in all examples are regularexperiment methods, except specially commented. All chemicals andmaterials are commercially obtained except specially commented.

The methods of chemical analysis and analytical instruments in presentinvention are described as following:

1. Determination of Intrinsic Viscosity (IV)

Industry standard method for determination of the PET: according to thesociety of the plastics industry (SPI's) on standard measurements of PETpolymer in phenol/1,1,2,2-four chloroethane (60:40 by weight) mixedsolution, with Ubbelohde viscometer, temperature for determination is25° C.

The degree of polymerization of PET is calculated by following formula:

DP _(n)=1.19×IV−7;

where the unit for IV is dL/g, therefore the chain length of polyestersof the present invention will be calculated in same methods.

2. Chemical Composition and Structure

The chemical structures in present invention are determined by NMR attemperature of 20° C. in solution with D substituted chloroform solvent(CDCl₃).

3. Thermal Properties Measurements

The thermal properties of polyester polymers prepared in the presentinvention are measured with Differential scanning calorimeter (DSC) Q20,manufactured by TA Instruments.

4. Degradation Measurements

The degradation measurement is weight loss percentage of polyesterpolymers prepared in present invention in 5% NaOH aqueous solution at100° C. with stirring for n hours.

5. Mechanical Property Test

Measurement of tensile strength is performed by Shanghai Institute ofOrganic Chemistry, Academia Sinica, according to ASTMD638-97 standardmethods.

EXAMPLE 1 1. Synthesis of Degradable Block: di-(methylhydroxyacetate)succinat(MeGSGMe)

To a solution of succinic acid (23.62 gram, 0.20 mole) and triethylamine(56 ml, 0.4 mole) in anhydrous acetonitrile (50 ml), add drop-wisemethyl bromoacetate (73.43 g, 0.48 mole). The solution is stirred atroom temperature for 5 hours and 100 ml more of anhydrous acetonitrileis added when the white precipitate shows up. After 24 hours reactionthe solution is filtrated to remove ammonium salt and the solventacetonitrile is removed in vacuum. The residue is under vacuum (3 mmHg)at 50° C. for 16 hours to remove extra methyl bromoacetate. The residuethen is dissolved in ethyl acetate (200 ml) and washed with DI water toremove trace amount of ammonium. The solvent was removed in vacuum afterdried with MgSO₄ and 41.43 gram solid degradable block, MeGSGMe, iscollected, yield: 79%. ¹HNMR (CDCl₃, 400 Mz) δ 4.66 (D, 4H); δ 3.77 (S,6H); δ 2.80 (T, 4H).

2. Synthesis of Polyester Polymers of the Present Invention

Bis(2-hydroxyethyl)terephthalate (BHET, 71.19 gram,) and di-(methylhydroxyacetate)succinate (degradable blocks MeGSGMe, 10.49 gram) (repeatunit molar ratio for BHET:MeGSGMe is 7:1) and 0.01 wt % Sb₂O₃ are placedin a stainless steel pressure reactor with a magnetic stirring bar andN2/vacuum purged three times and the vacuum is reduced to about 2 mmHg.The system is placed in a 275° C. oil bath for 5 hours with stirringunder vacuum. Dry ice is added to cool down the melt to room temperaturequickly. 57.2 gram solid is collected and that is the rapid degradablepolyester polymer described in the present invention, named as:mPET(MeGSGMe). The bulk solid is roughly grinded into small pieces andthe intrinsic viscosity is measured in phenol/1,1,2,2-tetrachloroethane(60/40 weight ratio) according to SPI's (The Society of PlasticIndustry) standard PET measurement procedure.

FIG. 1 is the DSC measurement (temperature raised at 10° C./min) for theabove synthesized polymer and shows its thermal properties. It can beobserved that the glass-transition temperature of the new polymer is 56°C., melting temperature is 216° C., the re-crystallization temperatureduring temperature rising is 121° C. FIG. 1 shows, due to the differentstructured degradable blocks which are embraced in polymer main chains,the crystallinity of the polyester polymers obtained in the presentinvention is reduced, and its melting temperature is much lower thanthat of regular PET. In addition, due to the embracement of degradableblocks, the soft segments of polyester chains are longer, that makes theglass-transition temperature of the polyester according to the presentinvention lower than that of regular PET.

The intrinsic viscosity of obtained polymer is measured as 0.57 dL/g inphenol/1,1,2,2 four chloroethane (60:40 weight ratio), based on thestandard measurement method of Society of Plastic Industry (SPI) forPET.

In addition, the calculation based on B. Gantillon's formula shows thedegree of polymerization for polyester synthesized in this example isequal to

DP _(n)=1.19×IV−7=1.19×(0.57×100)−7=61

the degree of polymerization for regular PET.

According to ASTMD638-97 standard, the Young's module for the polymersynthesized in this example is measured as 910 Mpa, the tensile stressis 57 MPa.

FIG. 2 shows the weight loss of synthesized polyester polymer at 100°C., 5% NaOH aqueous solution with stirring for n hours. From the figureit can be seen that the weight loss percentage of the polymersynthesized in this example reaches 49.78% after 120 minutes, 83.84%after 240 minutes, 92.24% after 480 minutes. This further demonstratesthe rapid degradability of polyester polymer synthesized in the presentinvention at given conditions.

EXAMPLE 2 1. Synthesis of Degradable Block: MeGSGMe

To a solution of succinic acid (23.62 g, 0.20 mol) and triethyl amine(84 mL, 0.6 mol) in methylene chloride (50 mL), add drop-wise methylchloroacetate (65.11 g, 0.6 mol) and stirred at room temperature for 5hours. When white precipitate appears, methylene chloride (100 mL) wasadded. The solution is stirred for 24 hours then the solid is removedthrough filtration. The filtrate was washed with water to remove residueamine, dried with anhydrous MgSO₄. The solvent CH₂Cl₂ was removed invacuum and 47.20 g solid, degradable block: MeGSGMe, is obtained; yield90%.

¹HNMR (CDCl₃, 400 Mz) δ 4.66 (D, 4H); δ 3.77 (S, 6H); δ 2.80 (T, 4H).

2. Synthesis of Non-Degradable Blocks: PET Oligmer

Bis(2-hydroxyethyl)terephthalate (BHET, 100 gram, 0.393 mol) and Sb₂O₃(0.02 gram) was placed in a 250 mL pressure reactor, purged withnitrogen gas three times and then was heated under vacuum for 45 minutesto 275° C.; the system is maintained under 3 mmHG vacuum at 275° C. fora various time period (2-7 hours), to obtain different PET oligmers withvarious viscosity. The obtained PET oligomers are measured for intrinsicviscosities in phenol/1,1,2,2 four chloroethane (60:40 weight ratio)mixed solution. FIG. 4 shows the co-relationship of intrinsic viscosityof PET oligomer vs polymerization time.

3. Synthesis of Polyester Polymers According to the Present Invention

The degradable blocks synthesized in step 1 is added into the PEToligomers synthesized in step 2 and then continue to polymerize at 275°C. for 1-3 hours and terminated at the given degree of polymerization(intrinsic viscosity). According to this method, polymers with differentmole ratio of degradable blocks/non-degradable blocks=1:5, 1:7, 1:9 andso on can be synthesized (i.e. t=5, 7, 9 . . . etc).

Table 1 is the results of mechanical property test for polymers in thisexample according to degradable blocks/non-degradable blocks mole ratio1:5, 1:7, 1:9.

TABLE 1 Characterization Results for Various Polymers degradableblocks/non- Young's Tensile degradable IV Tg Tm Module Stress blocks(dL/g) (° C.) (° C.) (MPa) (MPa) 1:5 0.61 54 199 890 57.5 1:7 0.57 56216 910 57.0 1:9 0.713 63 213 930 57.5

In summary, the polyester polymers provided by the present invention notonly have excellent mechanical processing properties but also can berapidly degraded at proper environment (such as alkaline solution) andtherefore effectively resolve the environment pollution problems causedby this kind of polymers. It satisfied the wide application demand andespecially it ensured such kind of polymers can be use for beveragebottle, food package film, shopping bag and other food packagecontainers. In addition, the method of preparation in present inventionis simple, low-cost, and the raw materials are easy to be obtained atlow price. It is suitable to volume production and has practical valueand application potentials.

Finally, it is necessary to claim here: the above examples are only usedto further detail the technical demonstration of the invention, cannotbe understand as limitations on the scope of the invention protected,anyone in this field makes any non-essential improvements andadjustments based on the contents of the invention will fall into thescope of protection of the invention.

1-12. (canceled)
 13. A polymer or copolymer having a form of (-AB—)_(n),made from poly-condensation of blocks A and blocks B in repeatedstructure units, wherein the block A has a structure of Formula (I):

the block B has a structure of Formula (II):

and the polymer or copolymer (-AB—)_(n) has a structure of Formula(III):

wherein p, m, s, r and u are integers greater than 0 but smaller than11; t is an integer greater than 1 but smaller than 31; n is an integergreater than 1; and R, R₁, R₂, R₃, R₄, R₅, R₆, R₇ in each of thestructural units are independently selected from H, substituted orun-substituted alkyl, substituted or un-substituted heteroalkyl,substituted or un-substituted cycloalkyl, substituted or un-substitutedheterocycloalkyl, substituted or un-substituted aryl and substituted orun-substituted heteroaryl, substituted or un-substituted alkoxy, ester,nitro, amine, amide, or thiol.
 14. The polymer or copolymer according toclaim 13, wherein R, R₁, R₂, R₃, R₄, R₅, R₆ in each of the structuralunits are independently selected from H or C₁-C₁₀ alkyls; R₇ is selectedfrom H, substituted or unsubstituted alkyl, substituted or unsubstitutedheteroalkyl, substituted or unsubstituted cycloalkyl, substituted orunsubstituted heterocycloalkyl, substituted or unsubstituted aryl. 15.The polymer or copolymer according to claim 14, wherein R, R₁, R₂, R₃,R₄, R₅, R₆ in each of the structural units are independently selectedfrom H or methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl;R₇ is selected from H, substituted or unsubstituted alkyl, substitutedor unsubstituted heteroalkyl, substituted or unsubstituted cycloalkyl,substituted or unsubstituted heterocycloalkyl.
 16. The polymer orcopolymer according to claim 14, wherein R is methyl; R₁, R₂, R₃, R₄,R₅, R₆, R₇ are H; p=2; m and s are any integer independently selectedfrom 1, 2, 3, 4 or 5; t is an integer greater than 1 but smaller lessthan 31; r=1 or 2; u=1 or 2; and n is an integer greater than
 2. 17. Amethod of making a polymer or copolymer according to claim 1, comprisingthe step of poly-condensation polymerization of the blocks A with theblocks B through solution polymerization or melting polymerization asfollows:


18. The method according to claim 17, further comprising the step ofsynthesizing the block B as follows:

wherein X is selected from Cl, Br, I, NH₂ or OH.
 19. The methodaccording to claim 17, further comprising the step of synthesizing theblock A in each structural unit as follows:


20. A method of making the polymer or copolymer according to claim 1,comprising the step of:


21. The method according to claim 20, further comprising the step ofsynthesizing

as follows:


22. The method according to claim 17, wherein the blocks B aresynthesized through melting condensation polymerization and the blocks Aare then added to the blocks B to continue, the melting condensationpolymerization.
 23. The method according to claim 20, wherein the blocksB are synthesized through melting condensation polymerization and theblocks A are then added to the blocks B to continue, the meltingcondensation polymerization.
 24. The method according to claim 22,wherein the melting condensation polymerization is carried out at240-290° C., under vacuum for 2-7 hours.
 25. The method according toclaim 23, wherein the melting condensation polymerization is carried outat 240-290° C., under vacuum for 2-7 hours.
 26. The method according toclaim 17, wherein the hydroxyl moles contained in the blocks B aregreater than the hydroxyl moles contained in the blocks A.
 27. Themethod according to claim 20, wherein the hydroxyl moles contained inthe blocks B are greater than the hydroxyl moles contained in the blocksA.
 28. The method according to claim 22, wherein the hydroxyl molescontained in the blocks B are greater than the hydroxyl moles containedin the blocks A.
 29. The method according to claim 23, wherein thehydroxyl moles contained in the blocks B are greater than the hydroxylmoles contained in the blocks A.
 30. A product containing a polymer orcopolymer according to claim
 1. 31. The product according to claim 30 isa beverage package bottle, food package films, shopping bags, or otherfood containers.